1. Field of the Invention
The present invention relates to a composite multilayered ceramic board in which plural kinds of multilayered ceramic boards are laminated, and to a method of manufacturing the same.
2. Description of the Background Art
As for mobile communication devices such as mobile telephones and portable communication terminals, smaller-sized devices have been highly required. Thus, smaller size and higher performance have also been required for high-frequency circuit boards used as internal components of such devices.
In order to satisfy such requirements, a multilayered ceramic board is employed for the high-frequency circuit board. The multilayered ceramic board has such construction that wiring patterns are formed on green sheets serving as the base of the ceramic board to form capacitance or inductance components thereon, without employing the technique that capacitors or inductors being components for use in surface mount are mounted on a printed circuit board. Since the multilayered ceramic board requires a smaller number of surface mount parts, the smaller-sized high-frequency circuit board is achieved.
The multilayered ceramic board is manufactured by forming wiring patterns on a plurality of green sheets mainly composed of alumina (Al2O3), laminating those green sheets, and sintering the whole of the laminated sheets at a temperature of from 800xc2x0 C. to 1600xc2x0 C. to integrate the sintered sheets as one.
FIGS. 7(a) and 7(b) are schematic perspective views showing a method of manufacturing a conventional multilayered ceramic board.
As shown in FIG. 7(a), first of all, predetermined wiring patterns 32A to 32D are formed, respectively, on green sheets 31A to 31D composed of alumina by screen printing. Then, as shown in FIG. 7(b), the green sheets 31A to 31D are laminated and sintered together at a temperature of from 800xc2x0 C. to 1600xc2x0 C. to form a multilayered ceramic board 30. Here, the green sheets are such sheets as made by mixing and kneading organic binders, ceramic raw material powders and the like, then processing the resultant mixture in the form of sheets and drying the processed sheets.
In the multilayered ceramic board 30, it is made possible to obtain capacitance or inductance in the internal portion of the multilayered ceramic board by forming the predetermined wiring patterns 32A to 32D on the green sheets 31A to 31D composed of alumina by screen printing. This makes it possible to reduce the number of capacitors or inductors being the surface mount components, enabling a decrease in the size of the components of the high-frequency circuit. Further, since the multilayered ceramic board 30 is formed of alumina exhibiting an insulation property as a main constituent, the board is suitable for forming resistance therein.
In the case where a multilayered ceramic board made of alumina with a smaller dielectric constant is substituted for a capacitor, the value of capacitance incorporated in the multilayered ceramic board is limited. Thus, if the value of capacitance is required to be obtained in a wide range, a capacitor being a component for use in surface mount is required. Alternatively, in the case where a multilayered ceramic board made of alumina without magnetism is substituted for an inductor, the value of inductance incorporated in the multilayered ceramic board is limited. Thus, if the value of inductance is required to be obtained in a wide range, an inductor or a transformer being a component for use in surface mount is required.
For example, if the value of capacitance and the value of inductance are required in a wide range, the number of components for use in surface mount can further be reduced by using a combination of a multilayered ceramic board composed of dielectric ceramics (hereinafter abbreviated as a dielectric multilayered ceramic board) and a multilayered ceramic board composed of magnetic ceramics (hereinafter abbreviated as a magnetic multilayered ceramic board) rather than using a multilayered ceramic board composed of an insulating ceramics (hereinafter abbreviated as an insulating multilayered ceramic board). A description will now be made on a method of combining the dielectric multilayered ceramic board and the magnetic multilayered ceramic board.
FIGS. 8(a) and 8(b) are schematic perspective views showing a manufacturing method of combining the dielectric multilayered ceramic board and the magnetic multilayered ceramic board.
With reference to FIG. 8(a), wiring patterns 42A to 42C are first formed on green sheets 41A to 41C made of dielectric ceramics by screen printing. Those green sheets are composed of, e.g., barium titanate (with a dielectric constant of 1400) (hereinafter abbreviated as dielectric green sheets). Wiring patterns 44A to 44C are formed on green sheets 43A to 43C composed of magnetic ceramics by screen printing. Those green sheets are composed of, e.g., a NiZn ferrite (with an initial magnetic permeability greater than 70, a magnetic flux density greater than 0.2T) (hereinafter abbreviated as magnetic green sheets).
Then, with reference to FIG. 8(b), the dielectric green sheets 41A to 41C and the magnetic green sheets 43A to 43C are laminated integrally, sintered together at a temperature of from 800xc2x0 C. to 1600xc2x0 C., so as to form a composite multilayered ceramic board 40.
In the composite multilayered ceramic board 40, the wiring patterns 42A to 42C formed on the green sheets 41A to 41C made of dielectric ceramics constitute a circuit mainly including a capacitance component. The wiring patterns 44A to 44C formed on the green sheets 43A to 43C made of magnetic ceramics constitute a circuit mainly including an inductance component. This makes it possible to obtain the value of capacitance and the value of inductance in a wide range. This enables a decrease in the number of capacitors and inductors being the components for use in surface mount and enables a decrease in the size of the components for use in the high-frequency circuit.
In the method of forming the composite multilayered ceramic board 40 by integrally laminating the dielectric green sheets 41A to 41C and the magnetic green sheets 43A to 43C and sintering the laminated sheets in whole, however, an internal stress densification phenomenon occurs which causes shrinkage of the materials for use in the multilayered ceramic boards, in a process that powders of the materials for use in the plurality of multilayered ceramic boards made of different materials are sintered in whole and grow to crystal grains. The shrinkage of the materials vary depending on the type, the thickness and the materials of the green sheets, and the mixing ratio of binders, the particle size and the shape of the material powders or the sintering conditions and the like.
FIG. 9 is a schematic cross-sectional view of the composite multilayered ceramic board 40 showing the sintering state of the board 40 having different shrinkage percentages. With reference to FIG. 9, the composite multilayered ceramic board 40 is formed of a dielectric multilayered ceramic board 41 and a magnetic multilayered ceramic board 43. Since this composite multilayered ceramic board 40 is formed by integrally laminating the dielectric multilayered ceramic board 41 and the magnetic multilayered ceramic board 43 which have different shrinkage percentages and then sintering the laminated boards in whole, deflection R is produced due to the shrinkage of materials.
FIG. 10 is an enlarged view of a joint portion of the dielectric multilayered ceramic board 41 and the magnetic multilayered ceramic board 43 shown in FIG. 9. With reference to FIG. 10(a), if no deflection R is caused by the shrinkage of materials, ideally, for example, no deviation is produced between a wiring pattern 42C formed on a dielectric multilayered ceramic board 41C and a via hole 44A formed on a magnetic multilayered ceramic board 43A. However, as shown in FIG. 10(b), if deflection R is caused by the shrinkage of materials, deviation "sgr" of wiring occurs between the wiring pattern 42C formed on the dielectric multilayered ceramic board 41C and the via hole 44A formed on the magnetic multilayered ceramic board 43A. The wiring deviation a causes an increase in electric resistance in the composite multilayered ceramic board 40, resulting in deterioration in circuit characteristics.
Thus, a description will now be made on a method of preventing the production of the wiring deviation. FIGS. 11(a) and 11(b) are schematic perspective views showing a manufacturing method of preventing the production of the wiring deviation "sgr" in a composite multilayered ceramic board.
With reference to FIG. 11(a), wiring patterns 42A to 42C are formed, respectively, on green sheets 41A to 41C made of dielectric ceramics by screen printing. Wiring patterns 44A to 44C are formed, respectively, on green sheets 43A to 43C made of magnetic ceramics by screen printing. Each one of the green sheets made of dielectric ceramics and each one of those made of magnetic ceramics are sintered one by one to form individual ceramic boards 45a to 45c and 48a to 48c. 
Those individual ceramic boards 45a to 45c and 48a to 48c are then cooled off. After the cooling, adhesives made of thermosetting resin such as polyimide and the like (hereinafter referred to adhesive layers) 46B, 46C, 47A to 47C are each applied on the respective upper faces of the individual ceramic boards 45b, 45c, 48a to 48c. Then, a part of the adhesive layers is removed so that the wiring patterns 42B, 42C, 44A to 44C formed on the individual ceramic boards 45b, 45c, 48a to 48c are electrically connected with each other.
Finally, the adhesive layers 46B, 46C, 47A to 47C are interposed between the individual ceramic boards 45a to 45c, 48a to 48c, respectively, and then the boards are laminated and joined with each other at a temperature of approximately 200xc2x0 C., so as to form a composite multilayered ceramic board 50.
Since the composite multilayered ceramic board 50 is constituted by joining the individual ceramic boards 45a to 45c, 48a to 48c one by one using the adhesive layers 46B, 46C and 47A to 47C, this makes it possible to inhibit the production of deviations between the layers of the composite multilayered ceramic board and prevent the wiring deviations "sgr". However, such a method of manufacturing the composite multilayered ceramic board results in a deterioration in the strength of the formed composite multilayered ceramic board in comparison with the case where the plurality of green sheets serving as the base of the ceramic board are laminated integrally and sintered in whole.
An object of the present invention is to provide a composite multilayered ceramic board having its deflection prevented and its strength increased and a method of manufacturing such a composite multilayered ceramic board.
A composite multilayered ceramic board according to one aspect of the present invention includes a first multilayered ceramic board formed by integrally sintering a plurality of green sheets that have a predetermined wiring pattern and are made of a first material, a second multilayered ceramic board formed by integrally sintering a plurality of green sheets that have a predetermined wiring pattern and are made of a second material that is different from the first material, and an adhesive layer formed between the first multilayered ceramic board and the second multilayered ceramic board.
In the composite multilayered ceramic board, since the first multilayered ceramic board is formed by integrally sintering a plurality of green sheets that have a predetermined wiring pattern and are made of the first material, this board has no deflection and the green sheets are firmly joined together, in comparison with a multilayered ceramic board formed by integrally sintering a plurality of green sheets that are made of different materials. Further, since the second multilayered ceramic board is formed by integrally sintering a plurality of green sheets that have a predetermined wiring pattern and are made of the second material that is different from the first material, this board has no deflection and the green sheets are firmly joined together, in comparison with the multilayered ceramic board formed by integrally sintering a plurality of green sheets made of different materials. In addition, since the adhesive layer is provided between the first and second multilayered ceramic boards, the production of deflection is prevented, leading to a decrease in electrical resistance caused by deviation of wiring patterns and to improved electrical circuit characteristics. This makes it possible to obtain such a composite multilayered ceramic board that has its deflection prevented and its strength increased.
One face of the first multilayered ceramic board may be joined to one face of the adhesive layer, and one face of the second multilayered ceramic board may be joined to the other face of the adhesive layer.
In that case, the first multilayered ceramic board and the second multilayered ceramic board are directly joined together by the adhesive layer.
The composite multilayered ceramic board further includes a wiring board, the adhesive layer includes a first adhesive layer and a second adhesive layer, and the wiring board is interposed between the first and second adhesive layers. In that case, one face of the first multilayered ceramic board may be joined to one face of the first adhesive layer. One face of the wiring board may be joined to the other face of the first adhesive layer. One face of the second multilayered ceramic board may be joined to one face of the second adhesive layer. The other face of the wiring board may be joined to the other face of the second adhesive layer.
In that case, the first and second multilayered ceramic boards are joined by the adhesive layer, with the wiring board interposed between those boards.
A partial region of the adhesive layer may be removed for the electrical connection between the wiring pattern of the first multilayered ceramic board and that of the second multilayered ceramic board.
In that case, the respective wiring patterns of the first and second multilayered ceramic boards are electrically connected to each other through the removed region of the adhesive layer.
The first material may include one of a dielectric material, a magnetic material and an insulating material, while the second material may include one of the dielectric material, magnetic material and insulating material.
In that case, a large capacitance component, a large inductance component or a large resistance component can be formed in the first or second multilayered ceramic board. This makes it possible to reduce the number of capacitors, inductors or resistors being components for use in surface mount, resulting in a smaller-sized composite multilayered ceramic board.
The first material may be a dielectric material, while the second material may be a magnetic material. In that case, multilayered ceramic board, while a large inductance component can be formed in the second multilayered ceramic board. This makes it possible to reduce the number of capacitors and inductors being components for use in surface mount, resulting in a smaller-sized composite multilayered ceramic board.
The first material may be a dielectric material, and the second material may be an insulating material. In that case, a large capacitance component can be formed in the first multilayered ceramic board, while a large resistance component can be formed in the second multilayered ceramic board. This makes it possible to reduce the number of capacitors and resistors being components for use in surface mount, resulting in a smaller-sized composite multilayered ceramic board.
The first material may be a magnetic material, and the second material may be an insulating material. In that case, a large inductance component can be formed in the first multilayered ceramic board, while a large resistance component can be formed in the second multilayered ceramic board. This makes it possible to reduce the number of inductors and resistors being the components for use in surface mount, leading to a smaller-sized composite multilayered ceramic board.
The adhesive layer may include a thermosetting resin. In that case, since the adhesive layer includes the thermosetting resin, heating facilitates its adhesion and setting, thereby enabling the formation of a composite multilayered ceramic board with excellent heat resisting properties.
A method of manufacturing a composite multilayered ceramic board according to one aspect of the present invention includes the steps of: laminating a plurality of green sheets that have a predetermined wiring pattern and are made of a first material and then sintering the laminated sheets so as to integrally form a first multilayered ceramic board, laminating a plurality of green sheets that have a predetermined wiring pattern and are made of a second material being different from the first material and then sintering the laminated sheets so as to integrally form a second multilayered ceramic board, and joining the first and second multilayered ceramic boards through an adhesive layer.
In accordance with the method of manufacturing the composite multilayered ceramic board, since the first multilayered ceramic board is formed by integrally sintering a plurality of green sheets that have a predetermined wiring pattern and are made of the first material, the board has no deflection and the green sheets are firmly joined together, in comparison with the multilayered ceramic board formed by integrally sintering a plurality of green sheets made of different materials. Since the second multilayered ceramic board is formed by integrally sintering a plurality of green sheets that have a predetermined wiring pattern and are made of the second material which is different from the first material, the board has no deflection and the sheets are firmly joined together, in comparison with the multilayered ceramic board formed by integrally sintering a plurality of green sheets made of different materials. Moreover, since the first and second multilayered ceramic boards are joined through the adhesive layer, the production of deflection is inhibited, thereby decreasing electrical resistance caused by the deviation of wiring patterns, resulting in improved electrical circuit characteristics. This makes it possible to obtain such a composite multilayered ceramic board that has its deflection prevented and its strength increased.
The step of joining the boards through the adhesive layer may include the step of joining one face of the first multilayered ceramic board to one face of the adhesive layer and joining one face of the second multilayered ceramic board to the other face of the adhesive layer.
In that case, the first and second multilayered ceramic boards are directly joined by the adhesive layer.
In case where the adhesive layer includes a first adhesive layer and a second adhesive layer, the step of joining the boards through the adhesive layer may include the steps of placing a wiring board between the first and second adhesive layers, joining one face of the first multilayered ceramic board and one face of the first adhesive layer, joining one face of the wiring board and the other face of the first adhesive layer, joining one face of the second multilayered ceramic board and one face of the second adhesive layer, and joining the other face of the wiring board and the other face of the second adhesive layer.
In that case, the first and second multilayered ceramic boards are joined by the adhesive layer with the wiring board interposed between those boards.
The method of manufacturing the composite multilayered ceramic board may further include the step of removing a partial region of the adhesive layer for the electrical connection between the respective wiring patterns of the first and second multilayered ceramic boards.
In that case, the respective wiring patterns of the first and second multilayered ceramic boards are electrically connected to each other through the removed region of the adhesive layer.
The first material is one of a dielectric material, a magnetic material and an insulating material, and the second material is one of the dielectric material, magnetic material and insulating material.
In that case, a large capacitance component, a large inductance component or a large resistance component can be formed in the first multilayered ceramic board or the second multilayered ceramic board, and the number of capacitors, inductors or resistors being components for use in surface mount can be reduced, resulting in a smaller-sized composite multilayered ceramic board.
The first material may be the dielectric material, while the second material may be the magnetic material. In that case, a large capacitance component can be formed in the first multilayered ceramic board, while a large inductance component can be formed in the second multilayered ceramic board. This makes it possible to reduce the number of capacitors and inductors being components for use in surface mount, leading to a smaller-sized composite multilayered ceramic board.
The first material may be the dielectric material, while the second material may be the insulating material. In that case, a large capacitance component can be formed in the first multilayered ceramic board, while a large resistance component can be formed in the second multilayered ceramic board. This makes it possible to reduce the number of capacitors or resistors being components for use in surface mount, enabling a smaller-sized composite multilayered ceramic board.
The first material may be the magnetic material, while the second material may be the insulating material. In that case, a large inductance component can be formed in the first multilayered ceramic board, while a large resistance component can be formed in the second multilayered ceramic board. This makes it possible to reduce the number of inductors and resistors being components for use in surface mount, resulting in a smaller-sized composite multilayered ceramic board.
The step of removing the partial region of the adhesive layer may include a photolithography step. In that case, since a portion of the adhesive layer is removed by the step of photolithography, the removal of the portion of the adhesive layer can be made in high accuracy.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.